Semiconductor device and method of manufacturing semiconductor device

Abstract

The present invention relates to a method of manufacturing a semiconductor device for forming an insulated gate field effect transistor in a completely isolated SOI layer, and has for its object to prevent depletion or inversion surely by introducing impurities of sufficiently high concentration into an SOI layer adjacent to an isolating film filled up between element regions of the SOI layer and a backing insulating layer and to aim at flattening of the SOI substrate surface, and further, includes the steps of implanting impurity ions into a semiconductor layer from an oblique direction so as to reach the semiconductor layer under an oxidation-preventive mask using the oxidation-preventive mask as a mask for ion implantation, heating the semiconductor layer in an oxidizing atmosphere with the oxidation-preventive mask so as to form a local oxide film to isolate the semiconductor layer, and also forming a impurity region with impurities implanted into the semiconductor layer in a region adjacent to the local oxide film and to at least an insulating layer under the semiconductor layer.

What is claimed is: 
     
       1. A semiconductor device comprising: an insulating layer formed on a first semiconductor layer;   a-second semiconductor layer, having a film thickness, formed on said insulating layer, wherein said second semiconductor layer gradually decreases in film thickness at a side edge of said second semiconductor layer so that a protrusion of said second semiconductor layer is formed on said insulating layer;   a local oxidation film formed by oxidizing a part of said second semiconductor layer, said local oxidation film being formed in contact with said protrusion of said second semiconductor layer;   a gate insulating film formed on said second semiconductor layer, said gate insulating film extending to said protrusion so as to directly cover at least a portion of said protrusion, and said gate insulating film being in contact with said local oxidation film; and   a gate electrode formed on said gate insulating film and in contact with said local oxidation film.